The invention relates to ink compositions in general, and ink jet ink compositions in particular. Ink jet printing is a well-known technique by which printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves the technique of projecting a stream of ink droplets to a surface and controlling the direction of the stream, e.g., electronically, so that the droplets are caused to form the desired printed message on that surface.
The technique of ink jet printing or non-contact printing is particularly well suited for application of characters onto irregularly shaped substrates and surfaces, including, for example, glass, metal, or plastic containers, generally used for holding beverage, cosmetic, pharmaceutical, liquor, and health care products.
The jetting of the ink droplets can be performed in several different ways. In a first type of process called continuous ink-jet printing, the ink stream jetted from an orifice of the print head is broken up, by applying a pressure wave pattern to this orifice, into ink droplets of uniform size and spacing. When the jet break-up mechanism is controlled, an electric charge can be applied to the droplets selectively and reliably as they form from the continuous ink stream. The charged drops passing through an electric field are deflected into a gutter for recuperation, while the uncharged drops proceed directly onto the ink-receiver to form an image or vice versa.
According to a second process the ink droplets can be created by a “drop on demand” method (DOD). A drop-on-demand device ejects ink droplets only when they are needed for imaging on the ink-receiver, thereby avoiding the complexity of drop charging, deflection hardware, and ink collection. In drop-on-demand ink-jet printing, the ink droplet can be formed by means of a pressure wave created by the mechanical motion of a piezoelectric transducer (the “piezo method”), or by means of discrete thermal pulses (the “bubble jet” method, or “thermal jet” method). In another mode of drop-on demand ink jet printing, the ink droplets are created by valves that open and shut independently to produce streams of intermittent ink droplets (the “valve jet” method).
In general, an ink composition should meet certain requirements to be useful for the intended purpose, for example, viscosity, electrical resistivity, solubility and compatibility of the components of the ink composition, and/or the wettability of the substrate by the ink composition. Further, the ink composition is preferably quick-drying and smear resistant. An ink jet ink composition should be capable of passing through the ink jet nozzle or nozzles without clogging and/or permit rapid cleanup of the machine components with minimum effort. The printed message should have good adhesion to the substrate and resist rubbing.
Quinone dyes have been proposed for use in ink jet ink compositions because of their light fastness and color reproduction characteristics. However, some of these ink compositions are water-based ink compositions as they contain water-soluble quinone dyes (e.g., anthraquinone dyes), and therefore, exhibit long ink dry times. Certain other qunione dyes, e.g, anthraquinone dyes, have limited solubility in organic solvents and tend to precipitate out of solution, especially at low temperatures, thereby clogging ink jet printer nozzle openings. There exists, therefore, a need for an ink jet ink composition comprising a quinone dye, which has short dry times and a reduced tendency to clog printer nozzle openings. The present invention provides such an ink composition. The advantages of the present invention as well as additional inventive features will be apparent from the description of the invention provided herein.